<template>
  <ul class="list">
    <li class="item"  v-for="item of letters" :key="item" :ref="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTuchEnd">{{item}}</li>
  </ul>
</template>
<script>
  export default {
    name:'CityAlphabet',
    props:{
      cities:Object
    },
    computed:{
      letters(){
        const letters = [];
        for(let i in this.cities){
          letters.push(i)
        }
        return letters;
      }
    },
    data(){
      return{
        touchStatus:false
      }
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText);
      },
      handleTouchStart(e){
        this.touchStatus = true;

      },
      handleTouchMove(e){
        if(this.touchStatus){
          const startY = this.$refs['A'][0].offsetY;
          const moveY = e.touches[0].clientY - 79;
          const index = Math.floor((startY - moveY)/ 20 );
          if(index >= 0 && index < this.letters.length){
            this.$emit('change',this.letters[index])
          }
        }
      },
      handleTuchEnd(){
        this.touchStatus = false;
      }
    }
  }
</script>
<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top:1.58rem
    right:0
    bottom:0
    width .4rem
    .item
      text-align center
      line-height .4rem
      color $bgColor
</style>
